build: add example bitcoin conf to win installer

Addresses
bitcoin#22235 (comment).

Author: fanquake

share/setup.nsi.in

@@ -75,6 +75,7 @@ Section -Main SEC0000
     File @abs_top_builddir@/release/@BITCOIN_GUI_NAME@@EXEEXT@
     File /oname=COPYING.txt @abs_top_srcdir@/COPYING
     File /oname=readme.txt @abs_top_srcdir@/doc/README_windows.txt
+    File @abs_top_srcdir@/share/examples/bitcoin.conf
     SetOutPath $INSTDIR\share\rpcauth
     File @abs_top_srcdir@/share/rpcauth/*.*
     SetOutPath $INSTDIR\daemon
@@ -129,6 +130,7 @@ Section /o -un.Main UNSEC0000
     Delete /REBOOTOK $INSTDIR\@BITCOIN_GUI_NAME@@EXEEXT@
     Delete /REBOOTOK $INSTDIR\COPYING.txt
     Delete /REBOOTOK $INSTDIR\readme.txt
+    Delete /REBOOTOK $INSTDIR\bitcoin.conf
     RMDir /r /REBOOTOK $INSTDIR\share
     RMDir /r /REBOOTOK $INSTDIR\daemon
     DeleteRegValue HKCU "${REGKEY}\Components" Main